This relates to a control for an excavator of the type in which an operator manually actuates joystick valves to supply hydraulic fluid to hydraulic control valves. The hydraulic control valves then in turn supply hydraulic fluid to hydraulic cylinders or motors to move the various excavator components. In a typical excavator, a boom extends from the excavator chassis, and is pivotally connected to a dipper stick. The dipper stick is pivotally connected to an excavator bucket or other excavator implement. The excavator chassis can be pivoted on the excavator undercarriage, typically by an hydraulic motor. The hydraulic cylinders pivot the boom with respect to the chassis, pivot the dipper stick with respect to the boom, and pivot the bucket or other excavator implement with respect to the dipper stick. Another common excavator configuration includes a second boom component which allows the boom to bend. This is often referred to as a variable angle boom or a VA boom, and permits work indoors or in areas having clearance restrictions, such as under power lines.
The operator of such an excavator manipulates joystick control levers which actuate the joystick valves to effect digging with the excavator bucket. The operator may be aided in this operation by a display in the cab of the excavator that shows the current elevation of the excavator bucket and the desired elevation of the worksite. Various sensors have been used to determine the bucket elevation, including laser sensors that sense a reference beam of laser light provided by a laser transmitter positioned at a distance from the excavator. GPS receivers also have been used to determine bucket elevation. Since the laser receivers and GPS receivers are typically not mounted directly on the excavator bucket, such receivers typically have been used to determine the location of a reference point on the excavator, and then the outputs from additional sensors, such as angle encoders and inclinometers, have been used to determine the position of the bucket relative to the reference point. A map of the desired contour of the worksite is typically stored in a memory associated with the excavator control so that the operator can be provided with a continuous display showing the amount of additional digging required to reach the desired elevation.
The skill and experience of excavator operators vary significantly, with the most skilled operators being able to dig to a final grade level much more quickly than those less skilled. Previous attempts at providing control of excavators had the system actively control one or more members of the excavator while the operator controlled the others. It was difficult for the operator to coordinate motions with the automatic systems which were slower than the operators and, effectively, the result was not as efficient as an operator digging without the automatic control. To dig to a desired contour or a line requires coordinated and constantly varied adjustment of the various members by the operator to maintain the cutting edge tangent to the desired path. Less experienced excavator operators have difficulty adequately coordinating the motions of the members simultaneously and may dig too deeply in some areas of the worksite, requiring that fill material be added to those areas later. It will be appreciated that returning fill material to the low areas of the worksite can be time consuming. Further, it may be necessary to compact the fill material in some instances, adding to the cost of the excavation operation. An excavator control and method are needed in which the efficiency of the operation of the machine is enhanced.